(1) Field of the Invention
The invention relates to a power transmission mechanism for placing between a driving shaft and two assemblies to be driven in such way that, as required, the first of said assemblies may or may not be driven, whereas the second assembly is permanently driven either by the driving shaft or by the first assembly.
On a gyroplane such as a helicopter, such a mechanism can be used for the transmission of the power supplied by at least one engine of the said helicopter to the rotors and to ancillary systems. While the ancillary systems such as the pump, alternator and similar type are permanently driven via a driving shaft, the rotors, driven via the same shaft, can be disengaged from the shaft while allowing for continued operation of the ancillary systems.
As a result of the use of such a power transmission mechanism, it is possible to use the single engine or one of the engines used for driving the gyroplane rotor or rotors to also drive the ancillary systems. This leads to a simplification and a weight gain of significant magnitude compared with the conventional arrangement, in which the ancillary systems are driven via a special auxiliary engine not used for driving the rotors. When the gyroplane is flying, the engine simultaneously drives the rotor or rotors, as well as the ancillary systems. In the case of a desired or undesired stoppage in flight of the engine or engines, the rotor or rotors operate under autorotation conditions and can continue to drive the ancillary systems. When the gyroplane is on the ground and in the absence of any external energy source, the transmission mechanism makes it possible for the engine to drive the ancillary systems providing the electric power and hydraulic power necessary for certain checking, repair and test operations, whilst the rotors are not rotating.
(2) Description of the Related Art
FR-A-1 422 328 describes a power transmission mechanism designed for fulfilling the above functions. This mechanism comprises three coaxial shafts, respectively connected to a driving shaft and to each of the two assemblies to be driven, and three free wheels connecting the shafts in pairs. Moreover, an actuator manipulatable from the gyroplane cockpit makes it possible to pass the free wheel placed between the driving shaft and the connection shaft of the rotor or rotors from a state where it joins these two shafts in rotation to a state where said two shafts are not joined. In the latter state, the rotor or rotors are not driven by the engine, whereas the ancillary systems are driven by the engine.
Although it fulfills the desired functions, the mechanism described in FR-A-1 422 328 is heavy and particularly complex. It also incorporates complicated locking devices for preventing damage to the mechanism if the engagement state changes are not performed when the rotation speeds of the different shafts are not perfectly synchronized.